The emerging electric vehicle and plug-in hybrid vehicle technologies mandate significant improvement of rechargeable battery technologies to achieve higher energy density. Despite the plentiful advantages, the overall energy density of lithium-ion batteries is limited by the low capacity of present cathode materials. Therefore, rechargeable batteries beyond lithium-ion have been widely investigated as alternatives. Among them, the lithium-sulfur battery (Li-SB) is an attractive technology for a number of reasons. For example, Li-SBs have a theoretical capacity of 1675 mAh and a very high specific energy density of about 2500 Wh kg-I, they are made with non-poisonous and abundant sulfur, and the LiSBs exhibit an intrinsic protection mechanism from overcharge due to soluble polysulfides, thereby providing an inherent measure of safety.
Despite the great promises, there still are a number of complex problems need to be solved for the commercialization of Li-SBs. Such problems include the formation of electrically insulating lithium polysulfides (Li2Sn) which can diffuse to the anode and directly react with Li metal to form lower order polysulfides including insoluble Li2S2 and Li2S, which will deposit on the Li anode. The lower order polysufides can also diffuse back to the cathode where they are oxidized to higher order polysulfides, thus forming an undesirable shuttle mechanism. Finally, Li-SBs tend to exhibit a rapid decrease in capacity during cycling, as well as high self-discharge rates.